The invention relates to analyzing an acquired arrangement of object locations.
The usefulness of a product expected to include items or attributes in a predetermined arrangement is diminished by a defect relating to the arrangement. If the product is meant to be a component in another product, this defect may ruin the other product.
For this reason, products incorporating such items or attributes in such predetermined arrangements may be inspected for compliance with some standard. Examples of products appropriate for inspection include ball grid array devices, micro-ball grid arrays, flip chips, and chip-scale packages (together called xe2x80x9cBGAsxe2x80x9d). The contacts (i.e., electrical terminals) of a BGA are metallic balls that are mounted on one side of the device for forming electrical connections between an integrated circuit within the BGA and a printed circuit board.
The standard used in the inspection is typically created by manual entry of coordinates, by xe2x80x9cgolden templatexe2x80x9d sampling, by derivation from computer-aided design (xe2x80x9cCADxe2x80x9d) data, or by some combination of these. According to the manual entry technique, a human operator uses a data entry device, such as a mouse or a keyboard, to specify x-y coordinates for the position of each object in the arrangement. Thus, manual entry can require considerable time. In golden template sampling, the positions of the objects in the standard are taken to be the positions found in an actual implementation of an ideal arrangement (e.g., an arrangement of balls of an actual BGA device). Golden template sampling may take less time than manual entry but may provide results that are less accurate. With respect to derivation from CAD data, the positions of the objects may be determined by software that automatically selects the positions in accordance with information about design goals, if such information is available.
In general, in one aspect, the invention features a method for analyzing an acquired arrangement of object locations that imperfectly conforms to an ideal arrangement of points. The method includes finding sets of vectors in the acquired arrangement of object locations, and deriving a composite set of vectors from the sets of vectors.
Implementations of the invention may include one or more of the following features. At least one of the object locations may represent an electrical terminal. The method may further include deriving an approximation of the ideal arrangement of points from the acquired arrangement of object locations, wherein the approximation includes an indication of whether an intersection specified by the composite set of vectors corresponds to an object location. The method may further include determining vectors between an object location and a number of the object location""s nearest neighboring points, or determining whether an object location matches, to an acceptable tolerance, a position specified by the composite set of vectors. The method may further include adjusting at least one of the vectors in the composite set to take into account a difference between the position specified and the actual position of the matching object location. The method may further include, based on the composite set of vectors and the actual position of the matching object location, specifying a location in which to search for another matching object location. The method may further include determining whether a non-matching object location matches, to an acceptable tolerance, another position specified by another composite set of the vectors.
In general, in another aspect, the invention features a system for detecting a pattern of discrete objects represented in an image. The system includes a location producer deriving an arrangement of object locations from the image, each object location representing an electrical terminal; a vectors producer deriving a set of vectors represented in the arrangement; a grid element producer deriving a two-vector grid element from the set of vectors; and a grid producer and grid element refiner testing the two-vector grid element against the arrangement of object locations and refining the two-vector grid element to take into account the actual positions of the object locations.
Among the advantages of the invention are one or more of the following. An effective approximation of an ideal regular pattern can be derived from a single golden template sample. Thus, in a case where direct information about the ideal pattern is unavailable (e.g., because CAD data is non-existent or inaccessible), the sample can be used as indirect information about the ideal pattern. In addition, the effective approximation can provide a standard that is sufficient for use in a quality control inspection system, which renders unnecessary the expense of time and resources involved in creating the standard by direct information. At least a portion of the standard can be stored in abbreviated form (e.g., a grid element to be repeated, and an on-off table), which can significantly reduce data storage requirements, especially in cases of large arrangements.
Other advantages and features will become apparent from the following description and from the claims.